1. Field of the Invention
The present invention relates to novel ceric oxide crystallite aggregates, and, more especially, to particular ceric oxide crystallite systems well suited for catalyzing the complete combustion of hydrocarbon fuels, in particular heavy fuels (gasoline, diesel fuel).
This invention also relates to the production of such novel aggregates and to the use thereof in reducing the emission of residues, e.g., soot and carbon particulates, from internal combustion engines.
2. Description of the Prior Art
During the combustion of diesel fuel in diesel engines, the carbon-containing products have a tendency to form soots which are reputed to be harmful both in respect of the environment and from a health and safety standpoint.
This art has long sought to reduce the emission of such carbon-containing particles, hereinafter simply designated by the expression "soots."
These efforts include the goal not to increase the emission of carbon monoxide or of gases considered to be toxic and mutagenic, such as the nitrogen oxides.
A wide variety of solutions have been proposed to reduce these carbon-containing emissions. One approach that is increasingly gaining in popularity is to equip the vehicular exhaust line with a filter, or soot trap, designed to trap all of the carbon-containing particles produced by combustion of the various combustible materials or fuels. Compare U.S. Pat. No. 4,621,593.
However, this technique is severely limited by the storage capacity of the filter which must be either emptied or incinerated. Such regeneration operation is extremely expensive to provide and to implement. One of the most commonly proposed solutions is the combustion of these soots, at particular intervals, either by electric heating or by using a fossil fuel igniter.
This particular technique nonetheless presents disadvantages, not the least of which is the risk of thermal shock giving rise to fracturing or cracking of the ceramic filter.
One solution which would be satisfactory would entail introducing catalysts into the soots which would initiate frequent self-ignition of the soots collected in the filter. To accomplish this, these soots must have a self-ignition temperature which is sufficiently low as to be frequently attained during normal running of, e.g., an internal combustion engine. Stated differently, it has been recognized that soot, collected from the exhaust gases of a diesel engine, can be more readily removed or eliminated by oxidation if the exhaust gas includes an agent which codeposits with the soot and depresses or catalyzes the ignition temperature of the soot.